The proposed research is designed to investigate age-related differences in sensitivity to anxiolytic effects of alcohol between the time of weaning and young adulthood. The immediate objectives are to understand the conditions under which alcohol may act as an effective anxiolytic unconditioned stimulus during different stages on ontogeny, and to identify specific developmental periods during which an organism may be more vulnerable to consequences of the drug. This information will provide a critical basis for subsequently examining how the timing of exposure to and learning about ethanol's anxiolytic effects early in life may control later alcohol-drinking patterns and contribute to the development of alcohol dependence. Toward achievement of these aims, two experimental paradigms used to measure anxiety that may be easily adapted for use with subjects of various ages were selected to assess potential ontogenetic differences in 1) initial sensitivity to any anxiolytic effects of alcohol, and 2) tolerance/sensitization to such effects with repeated drug exposure. Experiments 1 and 2 will examine the influence of a single acute administration of various mild doses of ethanol on the fear-potentiated startle response and elevated-plus maze performance of weanling (P23), periadolescent (P35), and adult (P75) rats. Using either of these two tasks, the third experiment will then examine how experience with alcohol via a sequence of prior daily administrations influences the anxiolytic action of the drug at the aforementioned ages.